This invention relates to a method of disposing of wastes containing heavy metal compounds by neutralizing the wastes, oxidizing the neutralized wastes, then solidifying the oxidized wastes using conventional mineral binding agents.
The disposal of liquid wastes by binding with conventional mineral binding agents, such as Portland cement, that set up to form insoluble solid wastes is well known in the art. U.S. Pat. No. 3,980,558 discloses the disposal of aqueous sludge from the manufacture of phosphoric acid containing soluble and insoluble arsenic with hydraulic cement to form a rock-like solid mass. The arsenic is entrapped in the solid and thereby prevented from being leached in the surrounding environment. No adjusting of pH is disclosed.
Japanese Kokai Patent No. Sho 47[1972]-31869 discloses the disposal of heavy metal containing wastes by adjusting the pH in the range of from 6.0 to 7.5 to precipitate heavy metals from plating waste water, then mixing with cement to form a solid mass.
U.S. Pat. No. 4,113,504 discloses the fixing of heavy metal containing sludge waste using vermiculite and cement. Two samples of arsenic containing sludge are adjusted to pH 11 using lime before being fixed.
U.S. Pat. No. 4,116,705 discloses the treating of hazardous waste with an aluminosilicate and a Portland cement to form a solid mass. For acidic samples, the desired mixing order of the hazardous waste is with the Portland cement first, then the aluminosilicate. No adjusting of pH is disclosed.
U.S. Pat. No. 4,118,243 discloses a method of disposing of arsenic containing wastes by reacting the aqueous waste with sulfuric acid and calcium hydroxide in the presence of sulfate ions and ferrous and/or ferric ions to form insoluble iron orthoarsenate and iron diarsenide. This procedure recommends that the mixture be a pH in the range of 4.0 to 10.5, since a lower pH causes an increase in the amount of arsenic in the leachate.
U.S. Pat. No. 4,142,912 discloses a method for treating arsenic containing wastes by mixing the wastes with Portland cement, sand, one or more water-soluble manganese or alkaline earth metal salts, and water to form a rock-like material. This patent teaches that the use of calcium hydroxide is inferior to the use of calcium chloride for decreasing leachability.
U.S. Pat. No. 4,149,968 discloses a method of treating aqueous hazardous industrial wastes by mixing the wastes with bentonite clays and Portland cement. One sample of steel pickling solution is pH adjusted to 12.0 using lime before treating, and a clarifier effluent from a sulfur dioxide scrubbing process is treated at an unadjusted pH of 5.5.
U.S. Pat. No. 4,329,179 discloses a method of treating arsenic containing wastes by mixing with a tricalcium aluminate-free hydraulic cement. No adjusting of pH is disclosed.
None of the above patents disclose the present method of disposing of wastes containing heavy metal compounds by neutralizing the wastes, oxidizing the neutralized wastes, then soldifying the oxidized wastes using conventional mineral binding agents. The present method provides a way of disposing of wastes containing heavy metals which effectively reduces the leaching of toxic materials in the surrounding environment, and thereby eliminates the polluting of underground water systems and surface waters.